1. Field of the Invention
The present invention relates to hearing aids. The invention more particularly relates to a hearing aid comprising a receiver and at least one first microphone for transforming an acoustic signal surrounding a hearing aid user into an electrical signal. The invention further relates to a method for estimating an air leak in an ear plug.
The invention is especially pertinent for a hearing aid comprising an ear plug part prepared for fitting tightly into the ear canal of a hearing aid user. The ear plug part comprises a second microphone arranged for transforming an acoustic signal in said volume into an electrical signal.
In the context of the present disclosure, a hearing aid should be understood as a small, microelectronic device designed to be worn behind or in an ear of a hearing-impaired user. The hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a microelectronic circuit comprising a signal processor, and an acoustic output transducer.
A Behind-The-Ear (BTE) hearing aid is worn behind the ear, and has a housing comprising the major electronics parts behind the ear and an earpiece, called ear plug in the following, for emitting sound to the hearing aid user. The ear plug is worn in the ear, e.g. in the concha or in the ear canal. In a traditional BTE hearing aid, a sound tube is used for conducting sound from a loudspeaker or receiver in the housing to the ear plug. In some types of hearing aids the receiver is arranged in the ear plug and is connected through electrical conductors to the housing behind the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This is known as Receiver-In-Canal (RIC) hearing aids.
In-The-Ear (ITE) hearing aids are designed for arrangement in the ear, normally in the funnel-shaped outer part of the ear canal. In a specific type of ITE hearing aids the hearing aid is placed substantially inside the ear canal. This type is known as Completely-In-Canal (CIC) hearing aids. This type of hearing aid requires a very compact design in order to allow it to be arranged in the ear canal, while accommodating the components necessary for operation of the hearing aid, such as microphones, a microelectronic circuit comprising a signal processor, an acoustic output transducer and a battery.
Hearing aids or ear plugs of hearing aids are made to fit tightly in the ear canal of the hearing aid user in order to achieve an optimum sound amplification without risk of feedback. The inner volume is the volume into which the receiver transmits sound in the inner part of the ear canal delimited by the ear plug or hearing aid.
Any need for air ventilation into the inner ear canal is taken care of by a well controlled ventilation channel, often referred to as a vent. The ventilation channel (or vent) is an intentional air leak between the volume in front of the ear drum limited by the ear plug or hearing aid, and the surroundings outside the ear canal. A ventilation channel has the advantage of reducing any occlusion effect (see explanation in WO-A1-2010/083888 page 1-3). The ventilation channel usually has a tubular shape, and the diameter is selected as a compromise between the wish to reduce occlusion and the need to obtain a sufficiently high sound pressure level at the ear drum.
For new hearing aid users it may be difficult to place the hearing aid or the hearing aid ear plug correctly in the ear canal and to verify that it is correctly placed. In the following, the term ear plug is used to refer to the part in the ear canal, whether it is an ear plug of a behind-the-ear hearing aid, an in-the-ear hearing aid or a completely-in-canal hearing aid. It may be difficult for new hearing aid users to detect if the hearing aid ear plug has changed position and is no longer correctly placed. If the hearing aid is not correctly placed in the ear canal an unintended air leak between the space in front of the ear drum and the surroundings may be formed. Such an air leak will increase the risk of feedback and it will reduce the sound pressure level at the ear drum. The benefits of the hearing aid will therefore be reduced.
This accidentally formed air leak is a non-intentional air leak. The sum of the intentional air leak and the non-intentional air leak is referred to as the effective air leak.
2. The Prior Art
US 2007/0019817 disclose a hearing aid which by playing an acoustic test signal can measure if the fitting of the hearing aid is correct. The test signal measured by a microphone is compared to a reference determined beforehand and stored in the hearing aid. If the test signal detected by the microphone deviates from the reference, information is given to an external unit that the fitting is not correct.
WO 2010/049543 discloses a method of measuring feedback of a hearing aid and, based on a comparison with feedback measured when the hearing aid is optimally fitted into the ear canal, deciding if the hearing aid is properly inserted in the ear canal of the hearing aid user.
US 2008/0123882 discloses a hearing aid which is automatically switched off when removed from the ear canal. The removal of the hearing aid is detected by generating an acoustic signal and detecting changes to the signal captured from this generated signal.
The problem of these known means for controlling the fitting of a hearing aid in the ear canal, or the removal of the hearing aid, is that they can only be applied for telling if the fitting is correct or not. Any more detailed information, such as if the fitting is far from being correct or if it is almost correct, cannot be obtained by these methods.